Building Materials, Third Edition

q RTS

4. (a) Describe setting and hardening of gypsum.
   (b) Give the salient features of keene’s and Mack’s cements.
   (c) How is Plaster of Paris manufactured?

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1. Consider the following statements regarding pure gypsum.
   
   
   1. It is translucent crystalline mineral
   
   
   2. It can be scratched by a finger nail
   
   
   3. When heated up to about 200°C its sp.gr increases from 2.3 to 2.95.
      Of the above the correct statements are:
      (a) 1 and 2 only (b) 1 and 3 only
      (c) 2 and 3 only (d) 1, 2 and 3
   
   
   
   


2. Gypsum has
   (a) high bulk density (b) negligible shrinkage
   (c) damp proofing property (d) low creep


3. Hardened gypsum
   (a) is fire resistant (b) can be used in places of high relative humidity
   (c) shrinks (d) has high bulk density


4. In metallurgical industries the moulds are manufactured from gypsum of variety having
   (a) —-modification (b) ˜-modification
   (c) hygrosocopicity (d) porus structure


5. The setting time of Plaster of Paris is delayed by adding retardant
   (a) cattle hair (b) clay
   (c) hydrated time (d) glue


6. Gypsum loses all its water of crystallization at about
   (a) 50° (b) 100°C
   (c) 200°C (d) 300°C


7. Plaster of Paris CaSO 4.^1
   2

H 2 O contains about

(a) 3% of water (b) 6% of water

(c) 8% of water (d) 11% of water

8. Keene’s Cement is made from
   (a) lime (b) slag
   (c) gypsum (d) puzzalana

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1. (d) 2. (b) 3. (a) 4. (a) 5. (d) 6. (c) 7. (b) 8. (c)